Titanium oxide particle, composition for forming photocatalyst, and photocatalyst

ABSTRACT

A titanium oxide particle includes a metal compound having a titanium metal atom and a carbon atom, and being bonded to a surface of the particle via an oxygen atom, wherein an element ratio (C/Ti) between carbon and titanium on the surface is in a range of 0.2 to 1.1 and the titanium oxide particle has an absorption at a wavelength of each of 450 nm and 750 nm in a visible absorption spectrum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2017-087541 filed Apr. 26, 2017.

BACKGROUND Technical Field

The present invention relates to a titanium oxide particle, acomposition for forming a photocatalyst, and a photocatalyst.

SUMMARY

According to an aspect of the invention, there is provided a titaniumoxide particle including:

a metal compound having a titanium metal atom and a carbon atom, andbeing bonded to a surface of the particle via an oxygen atom,

wherein an element ratio (C/Ti) between carbon and titanium on thesurface is in a range of 0.2 to 1.1; and

the titanium oxide particle has an absorption at a wavelength of each of450 nm and 750 nm in a visible absorption spectrum.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment which is an example of theinvention will be described.

Titanium Oxide Particle

Regarding a titanium oxide particle according to the exemplaryembodiment, a metal compound which includes a titanium atom and ahydrocarbon group is bonded to the surface thereof via an oxygen atom.The titanium oxide particle absorbs light having a wavelength of 450 nmand light having a wavelength of 750 nm in a visible absorptionspectrum. An element ratio C/Ti between carbon C and titanium Ti on thesurface thereof is 0.2 to 1.1.

The titanium oxide particle according to the exemplary embodiment issuitably used as a photocatalyst.

The titanium oxide particle according to the exemplary embodiment hasthe above configuration, and thus shows a high photocatalyst functioneven in the visible light region. The reason therefor is supposed asfollows.

Firstly, an untreated titanium oxide particle which is used as aphotocatalyst in the related art absorbs ultraviolet light, and thusshows a photocatalyst function (photocatalyst activity). Thus, theuntreated titanium oxide particle shows the photocatalyst functionduring a daytime on a sunny day on which ultraviolet light is ensured,but the photocatalyst function is degraded to insufficient levels duringa night-time or in the shade. For example, in a case where the untreatedtitanium oxide particle is used as an exterior wall material, adifference in stain resistance may often occur between a sunny place anda shade place. In a case where the untreated titanium oxide particle isused in an air cleaner, a water purifier, or the like, an additionalmounting space for example, mounting a black light or the like whichfunctions as a light source of an ultraviolet ray in the device may berequired.

Recently, titanium oxide particles which show the photocatalyst function(photocatalyst activity) by absorbing visible light are also known. Forexample, a titanium oxide particle obtained by adhering a different typeof metal (iron, copper, platinum, and the like) to titanium oxide, atitanium oxide particle obtained by doping a nitrogen element, a sulfurelement, and the like are known as a visible light-absorption typetitanium oxide particle.

On the other hand, a titanium oxide particle which shows the highphotocatalyst function even in a visible light region is required.

With respect to this, regarding to the titanium oxide particle accordingto the exemplary embodiment, a metal compound which includes a titaniumatom and a hydrocarbon group is bonded to the surface thereof via anoxygen atom. The titanium oxide particle absorbs light having awavelength of each of 450 nm and 750 nm in the visible absorptionspectrum. The element ratio C/Ti between carbon C and titanium Ti on thesurface thereof is 0.2 to 1.1.

The titanium oxide particle according to the exemplary embodiment isobtained, for example, in a manner as follows. The untreated titaniumoxide particle is subjected to a surface treatment with a metal compoundwhich includes a titanium atom and a hydrocarbon group. Then, at least aportion of the hydrocarbon group is oxidized by a heating treatment, andthus is changed to a C—O bond or a C═O bond. The detailed mechanism isnot clear. However, it is supposed as follows. That is, a structure inwhich a metal compound in which carbon atoms are adequately oxidized, anoxygen atom, and a titanium atom are joined in sequence by a covalentbond is provided on the surface of the titanium oxide particle. Thus,the surface of the titanium oxide particle shows light absorbency atwavelengths of 450 nm and 750 nm, and the titanium oxide particle showsvisible light responsiveness.

The element ratio C/Ti on the surface of the titanium oxide particle is0.2 to 1.1, and thus an amount of carbon in the hydrocarbon group andthe like on the surface of the titanium oxide particle is adequate.Light having a wavelength of each of 450 nm and 750 nm is sufficientlyabsorbed, and the high photocatalyst function is shown in the visiblelight region.

Specifically, since the element ratio C/Ti is in the above range, theadequate amount of the metal compound is bonded to the surface, and thusthe sufficient amount of light is absorbed at wavelengths of 450 nm and750 nm and the photocatalyst function in the visible light region isimproved, in comparison to a case where the element ratio C/Ti issmaller than the above range. Since the element ratio C/Ti is in theabove range, reduction of the exposed amount of an active portion oftitanium oxide and decomposition of the hydrocarbon group caused by anexcess amount of the metal compound bonded to the surface are preventedand the photocatalyst function in the visible light region is easilyobtained, in comparison to a case where the element ratio C/Ti isgreater than the above range.

From the above reasons, it is supposed that the titanium oxide particleaccording to the exemplary embodiment shows the high photocatalystfunction even in the visible light region, with the above configuration.

The metal compound which is bonded to the surface of the titanium oxideparticle according to the exemplary embodiment via an oxygen atomthereof is preferably at least one of a metal compound formed only by atitanium atom, a carbon atom, a hydrogen atom, and an oxygen atom and ametal compound formed by a titanium atom, a carbon atom, a hydrogenatom, an oxygen atom, and a phosphorus atom, from a viewpoint of moreeasily showing the visible light responsiveness. The metal compoundformed only by a titanium atom, a carbon atom, a hydrogen atom, and anoxygen atom is more preferable.

As the metal compound which is bonded to the surface of the titaniumoxide particle according to the exemplary embodiment via an oxygen atom,thereof, a compound which is bonded to the surface of the titanium oxideparticle via an oxygen atom O which is directly bonded to a titaniumatom Ti, that is, a compound which is bonded to the surface of thetitanium oxide particle by a covalent bond of Ti—O—Ti is preferableamong metal compounds, from a viewpoint of more easily showing thevisible light responsiveness.

Regarding the titanium oxide particle according to the exemplaryembodiment, from a viewpoint of more easily showing the visible lightresponsiveness, it is preferable that a metal compound which has atitanium, atom, and a hydrocarbon group bonded to the titanium atom viaan oxygen atom is bonded to the surface of the titanium oxide particlewith an oxygen atom interposed therebetween. That is, it is preferablethat a structure (C—O—Ti—O—Ti) in which a carbon atom C in thehydrocarbon group, an oxygen, atom O, a titanium, atom Ti in the metalcompound, an oxygen atom O, and a titanium atom Ti in the titanium oxideparticle are joined in sequence by a covalent bond is provided on thesurface of the titanium oxide particle. It is supposed that since thetitanium oxide particle according to the exemplary embodiment has theabove structure and the carbon atoms C are oxidized to a suitabledegree, the surface of the titanium oxide particle shows lightabsorbency at wavelengths of 450 nm and 750 nm and the titanium oxideparticle shows more visible light responsiveness.

The titanium oxide particle according to the exemplary embodiment isalso excellent from a viewpoint described below, in addition to a pointof showing the high photocatalyst function even in the visible lightregion.

Generally, an untreated titanium oxide particle has a low degree offreedom for controlling a particle diameter, particle diameterdistribution, and a shape of a particle, and has high particleaggregation. Thus, the titanium oxide particle does not have favorabledispersibility in a resin or a liquid, and there is a tendency that (1)showing of the photocatalyst function is difficult, (2) uniformity of acoated film formed with a coating liquid is low, and (3) transparency ofa film and the like is low.

However, the titanium oxide particle according to the exemplaryembodiment has favorable dispersibility because a hydrocarbon groupderived from the metal compound is provided on the surface of thetitanium oxide particle. Thus, a coated film is substantially uniformlyformed, and light hits the titanium oxide particle with high efficiency,and thus the photocatalyst function is easily shown. Transparency of afilm and the like, uniformity of a coated film of a coating liquid areimproved, and design properties are held. As a result, for example, whena coating material including the titanium oxide particle is applied ontothe surface of an outer wall material, a plate, a pipe, or non-wovenfabric (non-woven fabric of ceramic and the like), aggregation oftitanium oxide particles or an occurrence of coating defects isprevented, and the photocatalyst function is easily shown for a longterm.

Details of the titanium oxide particle according to the exemplaryembodiment will be described below.

Preferably, the titanium oxide particle according to the exemplaryembodiment is a titanium oxide particle obtained in a manner that anuntreated titanium oxide particle is subjected to a surface treatmentwith a metal compound which includes a titanium atom and a hydrocarbongroup, and then at least a portion of the hydrocarbon group is oxidizedby a heating treatment. In this disclosure, the metal compound whichincludes a titanium atom and a hydrocarbon group is also simply referredto as “a metal compound”.

Untreated Titanium Oxide Particle

In this disclosure, a titanium oxide particle which is not subjected toa surface treatment with a metal compound is referred to as “anuntreated titanium oxide particle”. Examples of the untreated titaniumoxide particle (titanium oxide particle as a target of a surfacetreatment) include particles of titanium oxide of a brookite type, ananatase type, a rutile type, or the like. The titanium oxide particlemay have a single crystal structure such as brookite, anatase, andrutile, or have a mixed crystal structure in which the above kinds ofcrystals are provided together.

The untreated titanium oxide particle in the exemplary embodiment is atitanium oxide particle which is not subjected to a surface treatmentwith a metal compound, and includes a titanium oxide particle which issubjected to other surface treatments. However, it is preferable thatthe titanium oxide particle according to the exemplary embodiment is atitanium oxide particle subjected to a surface treatment with only ametal compound.

A preparing method of the untreated titanium oxide particle is notparticularly limited. However, a chlorine method (vapor phase method),and a sulfuric acid method (liquid phase method) are exemplified.

An example of the chlorine method (vapor phase method) is as follows.Firstly, rutile ore as the raw material is caused to react with coke andchlorine. After gaseous titanium tetrachloride is obtained once, coolingis performed, thereby obtaining a titanium tetrachloride liquid. Then,after the titanium tetrachloride liquid is caused to react with oxygenat a high temperature, a chlorine gas is separated and thus, anuntreated titanium oxide is obtained.

An example of the sulfuric acid method (liquid phase method) is asfollows. Firstly, ilmenite ore (FeTiO₃) or titanium slag as the rawmaterial is dissolved in concentrated sulfuric acid, and an ironcomponent, which is an impurity, is separated in a form of iron sulfate(FeSO₄), thereby obtaining titanium, oxysulfate (TiOSO₄). Then, titaniumoxysulfate (TiOSO₄) is subjected to hydrolysis, and thus is precipitatedas titanium oxyhydroxide (TiO(OH)₂). Then, this precipitate is washedand dried. The resultant obtained by drying is baked, and thus,untreated titanium oxide is obtained.

In addition, as the preparing method of an untreated titanium oxideparticle, a sol-gel method using titanium alkoxide, a method of bakingmetatitanic acid, and the like are provided. The crystal structure of atitanium oxide particle is changed to brookite, anatase, or rutile inaccordance with the degree of the baking temperature (for example,heating in a range of 400° C. to 1,200° C.). Accordingly, a titaniumoxide particle having a desired crystal structure is obtained byadjusting the degree of the baking temperature.

Metal Compound

The “metal compound including a titanium atom and a hydrocarbon group”which is provided on the surface of the titanium oxide particleaccording to the exemplary embodiment is derived from a metal compoundused when a surface treatment is performed on the titanium oxideparticle.

A metal compound which includes a titanium atom and a hydrocarbon groupwhich is bonded to the titanium atom with an oxygen atom interposed(more preferably, with only one oxygen atom interposed) is preferable asthe metal compound used when a surface treatment is performed on thetitanium oxide particle. In a case where the metal compound includesplural hydrocarbon groups, at least one hydrocarbon group is preferablybonded to the titanium atom of the metal compound with an oxygen atominterposed (more preferably with only one oxygen atom interposed)between the hydrocarbon group and the titanium atom, from a viewpoint ofshowing the high photocatalyst function and improving dispersibility.

The hydrocarbon group may be bonded to the titanium atom of the metalcompound with a linking group other than the oxygen atom, which isinterposed. Examples of the linking group for linking the titanium atomof the metal compound to the hydrocarbon group include a phosphorus atomand a carbonyl group in addition to the oxygen atom, and the linkinggroup may be a single group among the groups or a group composed ofplural kinds of the groups.

Examples of the hydrocarbon group provided in the metal compound includea saturated aliphatic hydrocarbon group having 1 to 40 carbon atoms(preferably 1 to 20 carbon atoms, more preferably 1 to 18 carbon atoms,further preferably 4 to 12 carbon atoms, and particularly preferably 4to 10 carbon atoms), an unsaturated aliphatic hydrocarbon group having 2to 40 carbon atoms (preferably 2 to 20 carbon atoms, more preferably 2to 18 carbon atoms, further preferably 4 to 12 carbon atoms, andparticularly preferably 4 to 10 carbon atoms), and an aromatichydrocarbon group having 6 to 27 carbon atoms (preferably 6 to 20 carbonatoms, more preferably 6 to 18 carbon atoms, further preferably 6 to 12carbon atoms, and particularly preferably 6 to 10 carbon atoms).

From a viewpoint of showing the high photocatalyst function andimproving dispersibility, the hydrocarbon group is preferably analiphatic hydrocarbon group, more preferably a saturated aliphatichydrocarbon group, and particularly preferably an alkyl group. Thealiphatic hydrocarbon group may have any of a linear shape, a branchedshape, and a cyclic shape. However, from a viewpoint of dispersibility,a linear shape or a branched shape is preferable.

Examples of the saturated aliphatic hydrocarbon group include astraight-chain alkyl group (a methyl group, an ethyl group, a propylgroup, a butyl group, a pentyl group, a hexyl group, a heptyl group, anoctyl group, a nonyl group, a decyl group, a dodecyl group, a hexadecylgroup, an icosyl group, and the like); a branched alkyl group (anisopropyl group, an isobutyl group, an isopentyl group, a neopentylgroup, a 2-ethylhexyl group, a tertiary butyl group, a tertiary pentylgroup, an isopentadecyl group, and the like); and a cyclic alkyl group(a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, acycloheptyl group, a cyclooctyl group, a tricyclodecyl group, anorbornyl group, an adamantyl group, and the like).

Examples of the unsaturated aliphatic hydrocarbon group include analkenyl group (a vinyl group (ethenyl group), a 1-propenyl group, a2-propenyl group, a 2-butenyl group, a 1-butenyl group, a 1-hexenylgroup, a 2-dodecenyl group, a pentenyl group, and the like); and analkynyl group (an ethynyl group, a 1-propynyl group, a 2-propynyl group,a 1-butynyl group, a 3-hexynyl group, a 2-dodecynyl group, and thelike).

The aliphatic hydrocarbon group also includes a substituted aliphatichydrocarbon group. Examples of a substituent which may substitute thealiphatic hydrocarbon group include a halogen atom, an epoxy group, aglycidyl group, a glydoxv group, a mercapto group, a methacryloyl group,an acryloyl group, and a hydroxy group.

Examples of the aromatic hydrocarbon group include a phenylene group, abiphenylene group, a terphenylene group, a naphthalene group, and ananthracene group. The aromatic hydrocarbon group also includes asubstituted aromatic hydrocarbon group. Examples of a substituent whichmay substitute the aromatic hydrocarbon group include a halogen atom, anepoxy group, a glycidyl group, a glydoxy group, a mercapto group, amethacryloyl group, and an acryloyl group.

A titanium compound having a hydrocarbon group is exemplified as themetal compound. Specific examples of the titanium compound include atitanate coupling agent (for example, titanate ester and phosphite oftitanate ester) and titanium chelate.

Examples of the titanate coupling agent include isopropyl triisostearoyltitanate, tetraoctyl bis(ditridecyl phosphite)titanate, and bis(dioctylpyrophosphate)oxyacetate titanate.

Examples of titanium chelate include di-i-propoxy bis(ethylacetoacetate)titanium, di-i-propoxy bis(acetylacetonato)titanium,di-i-propoxy bis(triethanolaminate)titanium, di-i-propoxy titaniumdiacetate, and di-i-propoxy titanium dipropionate.

In addition to the above compounds, examples of the metal compoundinclude titanium coupling agents such as triethanolamine titanate,titanium acetylacetonate, titanium ethyl acetoacetate, titanium lactate,titanium lactate ammonium salt, tetrastearyl titanate, isopropyltricumyl phenyl titanate, isopropyltri(N-aminoethyl-aminoethyl)titanate, dicumyl phenyl oxyacetatetitanate, isopropyl trioctanoyl titanate, isopropyldimethacrylisostearoyl titanate, titanium lactate ethyl ester, octyleneglycol titanate, triisostearyl isopropyl titanate, isopropyl tridodecylbenzene sulfonyl titanate, tetra(2-ethylhexyl)titanate, butyl titanatedimer, isopropyl isostearoyl diacryl titanate, isopropyl tri(dioctylphosphate)titanate, isopropyl tris(dioctyl pyrophosphate)titanate,tetraisopropyl bis(dioctyl phosphite)titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl)phosphite titanate, bis(dioctylpyrophosphate)ethylene titanate, tetra-i-propyl titanate, tetra-n-butyltitanate, and diisostearoyl ethylene titanate.

The metal compound may be singly used or may be used in combination oftwo or more kinds thereof.

Characteristics of Titanium Oxide Particle

The titanium oxide particle according to the exemplary embodimentabsorbs light having wavelengths of 450 nm and 750 nm in a visibleabsorption spectrum.

From a viewpoint of showing the high photocatalyst function even in thevisible light region, it is preferable that the titanium oxide particleaccording to the exemplary embodiment absorbs light having wavelengthsof 450 nm, 600 nm, and 750 nm in the visible absorption spectrum. It ismore preferable that the titanium oxide particle absorbs light having awhole range of wavelengths of from 450 nm to 750 nm in the visibleabsorption spectrum. It is particularly preferable that the titaniumoxide particle absorbs light having a whole range of wavelengths of from400 nm to 800 nm in the visible absorption spectrum.

Regarding the titanium oxide particle, from a viewpoint of showing ahigh photocatalyst function even in the visible light region, in anultraviolet-visible absorption spectrum, when absorbance at a wavelengthof 350 nm is set to 1, the absorbance at a wavelength of 450 nm ispreferably 0.02 or more (preferably 0.1 or more). In addition, it ismore preferable that absorbance at a wavelength of 450 nm is 0.2 or more(preferably 0.3 or more), and absorbance at a wavelength of 750 nm is0.02 or more (preferably 0.1 or more).

The “absorbing light at wavelengths of 450 nm and 750 nm” means thatabsorbance at a wavelength of 450 nm is 0.005 or more and absorbance ata wavelength of 750 nm is 0.005 or more in an ultraviolet-visibleabsorption spectrum when absorbance at a wavelength of 350 nm is set to1.

The ultraviolet-visible absorption spectrum, is measured by a methodshown below. Firstly, titanium oxide particles which are a measurementtarget are dispersed in tetrahydrofuran, and then are applied onto aglass substrate. Then, drying is performed at 24° C. in the air.Regarding measurement, the measurement is performed in diffusereflection, arrangement, and theoretical absorbance is obtained byKubelka-Munk conversion. Regarding a diffuse reflection spectrum,measurement is performed in a range of wavelengths of from 200 nm to 900nm by using reflectance, and by using a spectrophotometer (U-4100manufactured by Hitachi High-Technologies Corporation) [measurementunder measurement conditions of; a scan speed of 600 nm, a slit width of2 nm, a sampling interval of 1 nm, and total reflectance measurementmode], Then, Kubelka-Munk conversion is performed, thereby a visibleabsorption spectrum is obtained.

Regarding the titanium oxide particle according to the exemplaryembodiment, the element ratio C/Ti on the surface is from 0.2 to 1.1.

Specifically, for example, from a viewpoint of showing the highphotocatalyst function even in the visible light region, the titaniumoxide particle has an element ratio C/Ti on the surface, which ispreferably from 0.3 to 1.0, more preferably from 0.4 to 0.9, andparticularly preferably from 0.5 to 0.8.

From a viewpoint of showing the high photocatalyst function even in thevisible light region, regarding the titanium oxide particle, the valueof the element ratio O/Ti between oxygen O and titanium Ti on thesurface thereof is preferably from 2.05 to 2.5, more preferably from 2.1to 2.45, and further preferably 2.15 to 2.4.

The value of the element ratio O/Ti between oxygen O and titanium Ti onthe surface of a general titanium oxide particle which is subjected to asurface treatment with the metal compound is equal to or slightlysmaller than 2.0. However, regarding the titanium oxide particleaccording to the exemplary embodiment, there is a high tendency that thevalue of the element ratio O/Ti between oxygen O and titanium Ti on thesurface of the titanium oxide particle is from 2.05 to 2.5. It isconsidered that this is because the hydrocarbon group on the surface ofthe titanium oxide particle is adequately carbonized. Thus, light atwavelengths of 450 nm and 750 nm is sufficiently absorbed, and the highphotocatalyst function in the visible light region is shown.

Since the element ratio O/Ti is in the above range, the hydrocarbongroup on the surface of the titanium oxide particle is sufficientlycarbonized. Thus, light having a wavelength of each of 450 nm and 750 nmis highly absorbed and the photocatalyst function in the visible lightregion is easily shown, in comparison to a case where the element ratioO/Ti is smaller than the above range. In addition, since the elementratio O/Ti is in the above range, reduction of the exposed amount of anactive portion of titanium oxide and decomposition of the hydrocarbongroup caused by an excess amount of the oxygen atoms bonded to thesurface are prevented and the photocatalyst function in the visiblelight region is easily shown, in comparison to a case where the elementratio O/Ti is greater than the above range.

The element ratio C/Ti and the element ratio O/Ti on the surface of thetitanium oxide particle are measured by a method shown below. Firstly,measurement is performed on a titanium oxide particle which is ameasurement target. The measurement is performed by using an X-rayphotoelectron spectroscopy (XPS) analyzer (JPS-9000MX manufactured byJEOL Corp.) under conditions that a MgKα beam is used as an X-raysource, an acceleration voltage is set to 10 kV, and an emission currentis set to 20 mA. The values of the element ratio C/Ti and the elementratio O/Ti are calculated from intensity of a peak of each element.

In the exemplary embodiment, it is preferable that the reduced amount ofthe element ratio C/Ti on the surface of the titanium oxide particle ina case where the titanium oxide particle is irradiated with anultraviolet ray having a wavelength of 352 nm and irradiation intensityof 1.3 mW/cm² for 20 hours is from 0.1 to 0.9.

The reduced amount of the element ratio C/Ti on the surface of thetitanium oxide particle in a case where the titanium oxide particle isirradiated with an ultraviolet ray having a wavelength of 352 nm andirradiation intensity of 1.3 mW/cm² for 20 hours is also referred to as“the reduced amount of the element ratio C/Ti by irradiation with anultraviolet ray” or “the reduced amount of the element ratio C/Ti”below. The reduced amount of the element ratio C/Ti by irradiation withan ultraviolet ray indicates a value obtained by subtracting the elementratio C/Ti measured after irradiation with an ultraviolet ray, from thevalue of the element ratio C/Ti measured before the irradiation with anultraviolet ray.

In the titanium oxide particle which satisfies the reduced amount of theelement ratio C/Ti by irradiation with an ultraviolet ray, the reducedamount of the element ratio C/Ti has a value which is greater than that,of a general titanium oxide particle subjected to a surface treatmentwith a metal compound or that of an untreated titanium oxide particle.Thus, the amount of carbon in the hydrocarbon group and the like or theamount of carbon obtained by carbonizing hydrocarbon, on the surface ofthe titanium oxide particle, is adequate. Light having a wavelength ofeach of 450 nm and 750 nm is sufficiently absorbed, and the improvedphotocatalyst function is shown in the visible light region. Since thehydrocarbon group and the like on the surface of the titanium oxideparticle are adequately decomposed by photocatalyst activity of thetitanium oxide particle, deterioration of a binder or a base material isprevented.

That is, since the reduced amount of the element ratio C/Ti is in theabove range, decomposition and separation from the titanium oxideparticle of carbon in the hydrocarbon group and the like or carbonobtained by carbonizing hydrocarbon, on the surface of the titaniumoxide particle, which occurs by photocatalyst activity, is prevented incomparison to a case where the range of the reduced amount of theelement ratio C/Ti is higher than the above range. Thus, deteriorationof the photocatalyst function in the visible light region is prevented.Since the reduced amount of the element ratio C/Ti is in the aboverange, the amount of carbon on the surface of the titanium oxideparticle is large. Thus, sufficient absorption of light having awavelength of each of 450 nm and 750 nm is easily obtained, and thephotocatalyst function is easily obtained in the visible light region,in comparison to a case where the element ratio C/Ti is lower than theabove range. Since the hydrocarbon group and the like on the surface ofthe titanium oxide particle are decomposed to a certain degree,deterioration of the binder or the base material is prevented.

From a viewpoint of showing the high photocatalyst function even in thevisible light region, the reduced amount of the element ratio C/Ti onthe surface of the particle, which occurs by irradiation with anultraviolet ray, is more preferably from 0.2 to 0.85, and furtherpreferably from 0.25 to 0.8.

The volume average particle diameter of the titanium oxide particlesaccording to the exemplary embodiment is preferably 10 nm to 1 μm, morepreferably 10 nm to 200 nm, and further preferably 15 nm to 200 nm. Ifthe volume average particle diameter of the titanium oxide particles is10 nm or more, aggregation of the titanium oxide particles is difficult,and the photocatalyst function is easily improved. If the volume averageparticle diameter of the titanium oxide particles is 1 μm or less, apercentage of a specific surface area to an amount is increased, and thephotocatalyst function is easily improved. Thus, if the volume averageparticle diameter of the titanium oxide particles is set to be in theabove range, a high photocatalyst function is easily shown in thevisible light region.

The volume average particle diameter of the titanium oxide particles ismeasured by using a dynamic light scattering type particle diametermeasuring device (for example, NANOTRACK UPA-ST manufactured byMicrotrac Bel Corporation). Regarding a measurement condition, aconcentration of a sample is set to be 20%, and a measurement period isset to be 300 seconds. The dynamic light scattering type particlediameter measuring device measures a particle diameter by using aBrownian motion in dispersoid. The device irradiates a solution with alaser beam, and detects scattered light, so as to measure a particlediameter. Cumulative distribution of a volume of each particle from asmall particle diameter side, in a divided particle diameter range(channel) is drawn based on particle diameter distribution which ismeasured by the dynamic light scattering type particle diametermeasuring device. Then, a particle diameter corresponding to theaccumulation of 50% is obtained as a volume average particle diameter.

Preparing Method of Titanium Oxide Particle

A preparing method of the titanium oxide particle according to theexemplary embodiment is not particularly limited. However, it ispreferable that the preparing method includes a process of performing asurface treatment on an untreated titanium oxide particle with a metalcompound, and a process of heating the titanium oxide particle during orafter the process of performing a surface treatment on the untreatedtitanium oxide particle.

Process of Performing Surface Treatment

A method of performing a surface treatment on an untreated titaniumoxide particle with a metal compound is not particularly limited.Examples of the method include a method in which a metal compound itselfis directly brought into contact with an untreated titanium oxideparticle; and a method in which a treatment liquid in which the metalcompound is dissolved in a solvent is brought into contact with anuntreated titanium oxide particle. Specific examples thereof include amethod in which a metal compound itself or a treatment liquid is addedto a dispersion in which untreated titanium oxide particles aredispersed in a solvent, under stirring; and a method in which a metalcompound itself or a treatment liquid is added (dropped, injected, orthe like) to an untreated titanium oxide particle in a state of flowingby stirring of HENSCHEL MIXER and the like. With the above methods, areactive group (for example, a hydrolyzable group such as a halogengroup and an alkoxy group) in the metal compound reacts with a hydroxylgroup provided on the surface of an untreated titanium oxide particle.Thus, the surface treatment of the untreated titanium oxide particle isperformed.

Examples of a solvent, for dissolving the metal compound include anorganic solvent (for example, hydrocarbon solvent, ester solvent, ethersolvent, halogen solvent, and alcohol solvent), water, and a mixedsolvent thereof.

Examples of the hydrocarbon solvent include toluene, benzene, xylene,hexane, octane, hexadecane, and cyclohexane. Examples of the estersolvent include methyl acetate, ethyl acetate, isopropyl acetate, andamyl acetate. Examples of the ether solvent include dibutyl ether anddibenzyl ether. Examples of the halogen solvent include1,1-dichloro-1-fluoroethane, 1,1-dichloro-2,2,2-trifluoroethane,1,1-dichloro-2,2,3,3,3-pentafluoropropane, chloroform, dichloroethane,and carbon tetrachloride. Examples of the alcohol solvent includemethanol, ethanol, and i-propyl alcohol. Examples of the water includetap water, distilled water, and pure water.

As the solvent, a solvent such as dimethylformamide, dimethylacetamide,dimethylsulfoxide, acetic acid, and sulfuric acid may be used inaddition to the above solvents.

In the treatment liquid in which the metal compound is dissolved in asolvent, concentration of the metal compound is preferably 0.05 mol/L to500 mol/L, and more preferably 0.5 mol/L to 10 mol/L.

Regarding conditions for a surface treatment of a titanium oxideparticle with the metal compound, from a viewpoint of showing a highphotocatalyst function and improving dispersibility, the followingconditions may be provided. An untreated titanium oxide particle may besubjected to a surface treatment with a metal compound which is from 10parts by weight to 100 parts by weight (preferably from 20 parts byweight to 75 parts by weight, and more preferably from 25 parts byweight to 50 parts by weight), with respect to 100 parts by weight ofthe untreated titanium oxide particle. If the amount of the metalcompound is set to be 10 parts by weight or more, the high photocatalystfunction is more easily shown even in the visible light region anddispersibility is easily improved. If the amount of the metal compoundis set to be 100 parts by weight or less, an occurrence of a situationin which the amount, of metal which is derived from the metal compoundand is provided on the surface of the titanium oxide particle becomesexcessive is prevented and deterioration of the photocatalyst functioncaused by the surplus metal is prevented.

A temperature of the surface treatment of an untreated titanium oxideparticle with the metal compound is preferably from 15° C. to 150° C.,and more preferably from 20° C. to 100° C. A surface treatment period ispreferably from 10 minutes to 120 minutes, and more preferably from 30minutes to 90 minutes.

After the surface treatment of an untreated titanium oxide particle withthe metal compound, a drying treatment may be performed. A method of thedrying treatment is not particularly limited. For example, a knowndrying method such as a vacuum drying method and a spray drying methodis applied. A drying temperature is preferably from 20° C. to 150° C.

Process of Performing Heating Treatment

The heating treatment is performed in the middle of the process ofperforming a surface treatment on an untreated titanium oxide particleor performed after the process of performing a surface treatment on anuntreated titanium oxide particle.

The heating treatment may be separately performed when the untreatedtitanium oxide particle is subjected to a surface treatment with themetal compound; when a drying treatment is performed after the surfacetreatment; or after the drying treatment. From a viewpoint of improvingreactivity of the titanium oxide particle with the metal compound beforethe heating treatment is performed, it is preferable that the heatingtreatment is separately performed when a drying treatment is performedafter the surface treatment or is separately performed after the dryingtreatment. From a viewpoint of suitably performing the drying treatment,it is preferable that the heating treatment is separately performedafter the drying treatment.

From a viewpoint of showing a high photocatalyst function and improvingdispersibility, a temperature of the heating treatment is preferably180° C. to 500° C., more preferably 200° C. to 450° C., and furtherpreferably 250° C. to 400° C.

From a viewpoint of showing the high photocatalyst function andimproving dispersibility, a period for the heating treatment ispreferably from 10 minutes to 300 minutes, and more preferably from 30minutes to 120 minutes.

In a case where the heating treatment is performed in the middle of theprocess of performing a surface treatment on an untreated titanium oxideparticle, it is preferable that, firstly, the metal compound is causedto sufficiently react at the temperature of the surface treatment, andthen the heating treatment is performed at the temperature of theheating treatment. In a case where the heating treatment is performedduring the drying treatment after the surface treatment, the temperatureof the drying treatment is used as the temperature of the heatingtreatment.

Since the temperature of the heating treatment is set to be from 180° C.to 500° C., titanium oxide particles that show the high photocatalystfunction even in the visible light region are effectively obtained. Thereason is supposed as follows. If the heating treatment is performed ata temperature of 180° C. to 500° C., the hydrocarbon group which isprovided on the surface of the titanium oxide particle and is derivedfrom the metal compound is adequately oxidized. Thus, some of C—C bondsor C═C bonds are changed to C—O bonds or C═O bonds.

The heating treatment is preferably performed in an atmosphere in whichoxygen concentration (volume %) is from 1% to 21%. Since the heatingtreatment is performed in this oxygen atmosphere, the hydrocarbon groupwhich is provided on the surface of the titanium oxide particle and isderived from the metal compound is adequately oxidized with highefficiency. The oxygen concentration (volume %) is more preferably from3% to 21%, and further preferably from 5% to 21%.

A method of the heating treatment is not particularly limited. A knownheating method, for example, heating by an air furnace, a kiln (rollerhearth kiln, shuttle kiln, or the like), a radiant heating furnace, orthe like; or heating by a laser beam, an infrared ray, UV, a microwave,or the like is applied.

With the above processes, the titanium oxide particle according to theexemplary embodiment is appropriately obtained.

Composition for Forming Photocatalyst

A composition for forming a photocatalyst according to the exemplaryembodiment includes the titanium oxide particle according to theexemplary embodiment and at least one compound selected from the groupconsisting of a dispersion medium and a binder.

Examples of an aspect of the composition for forming a photocatalystaccording to the exemplary embodiment include a dispersion whichincludes the titanium oxide particle according to the exemplaryembodiment and a dispersion medium; and a composition which includes thetitanium oxide particle according to the exemplary embodiment, and anorganic or inorganic binder. The dispersion may have a paste shapehaving high viscosity.

As the dispersion medium, water, an organic solvent, and the like arepreferably used.

Examples of the water include tap water, distilled water, and purewater.

The organic solvent is not particularly limited, and for example, ahydrocarbon solvent, an ester solvent, an ether solvent, a halogensolvent, and an alcohol solvent are exemplified.

From a viewpoint of dispersion stability and storage stability, thedispersion preferably contains at least one compound selected from thegroup consisting of a dispersing agent and a surfactant. As thedispersing agent and the surfactant, known chemical materials are used.The dispersion may include a binder in a form of an emulsion.

The binder used in the composition is not particularly limited. Examplesof the binder include an organic binder such as fluorine resin, siliconeresin, polyester resin, acrylic resin, styrene resin,acrylonitrile/styrene copolymer resin, acrylonitrile/butadiene/styrenecopolymer (ABS) resin, epoxy resin, polycarbonate resin, polyamideresin, polyamine resin, polyurethane resin, polyether resin, polysulfideresin, polyphenol resin, a compound thereof, and resin obtained bysilicone-modifying or halogen-modifying the above resins; and aninorganic binder such as a glass, ceramic, or metal powder.

The composition for forming a photocatalyst according to the exemplaryembodiment may contain other components other than the above-describedcomponents. Known additives are used as the other components, forexample, a promoter, a coloring agent, a filler, an antiseptic agent, adefoaming agent, an adhesion-enhancing agent, and a thickening agent areexemplified.

The composition for forming a photocatalyst according to the exemplaryembodiment may singly contain the titanium oxide particle according tothe exemplary embodiment or may contain two or more types of titaniumoxide particles.

In the composition for forming a photocatalyst according to theexemplary embodiment, the content of the titanium oxide particleaccording to the exemplary embodiment is not particularly limited, andmay be appropriately selected in accordance with various aspects such asa dispersion and a resin composition, and a desired amount of thephotocatalyst.

A preparing method of a photocatalyst using the composition for forminga photocatalyst according to the exemplary embodiment, or a preparingmethod of a structure having the photocatalyst is not particularlylimited, and well-known applying methods are used.

Examples of the applying method of the composition for forming aphotocatalyst according to the exemplary embodiment include a spincoating method, a dip coating method, a flow coating method, a spraycoating method, a roll coating method, a brush coating method, a spongecoating method, a screen printing method, and an ink jet printingmethod.

Photocatalyst and Structure

A photocatalyst according to the exemplary embodiment includes thetitanium oxide particle according to the exemplary embodiment.

A structure according to the exemplary embodiment contains the titaniumoxide particle according to the exemplary embodiment.

The photocatalyst according to the exemplary embodiment may be aphotocatalyst formed only from the titanium oxide particle according tothe exemplary embodiment, be a photocatalyst obtained by mixing apromotor to the titanium oxide particle according to the exemplaryembodiment, or be a photocatalyst obtaining in a manner that thetitanium oxide particle according to the exemplary embodiment issolidified by an adhesive agent or a tacky agent, so as to have adesired shape.

The structure according to the exemplary embodiment preferably has thetitanium oxide particle according to the exemplary embodiment, as aphotocatalyst. From a viewpoint of photocatalyst activity, the structureaccording to the exemplary embodiment preferably has the titanium oxideparticle according to the exemplary embodiment, on at least the surface.

The structure according to the exemplary embodiment is preferably astructure in which the titanium oxide particle according to theexemplary embodiment is provided at least at a portion of the surface ofa base material, and is preferably a structure formed by applying thecomposition for forming a photocatalyst according to the exemplaryembodiment, to at least a portion of the surface of the base material.In the structure, the amount of the applied composition for forming aphotocatalyst according to the exemplary embodiment is not particularlylimited, and may be selected in accordance with a desire.

In the structure according to the exemplary embodiment, the titaniumoxide particle according to the exemplary embodiment may be adhered orfixed to the surface of the base material. However, from a viewpoint ofdurability of the photocatalyst, the titanium oxide particle ispreferably fixed to the surface of the base material. A fixing method isnot particularly limited, and well-known fixing methods are used.

As a base material used in the exemplary embodiment, various materialsare exemplified regardless of an inorganic material and an organicmaterial. The shape of the base material is also not limited.

Preferable examples of the base material include metal, ceramic, glass,plastic, rubber, stone, cement, concrete, textile, fabric, wood, paper,and combination thereof, a stacked member thereof, and an object inwhich at least one coated film is provided on the surface of the abovematerial.

Preferable examples of the base material considered from a viewpoint ofa use include a building material, an exterior material, a window frame,window glass, a mirror, a table, dishes, a curtain, a lens, a prism,exterior and painting of a vehicle, facing of a mechanical device,facing of a product, a dustproof cover and painting, a traffic sign,various display devices, an advertising tower, a sound insulation wallfor road, a sound insulation wall for railway, a bridge, exterior andpainting of a guard rail, interior and painting of a tunnel, aninsulator, a solar cell cover, a solar water heater collector cover, apolymer film, a polymer sheet, a filter, an indoor signboard, an outdoorsignboard, a vehicle lighting lamp cover, an outdoor lighting equipment,an air purifier, a water purifier, medical equipment, and a nursing careproduct.

EXAMPLES

The present invention will be more specifically described by usingexamples. However, the examples do not limit the present invention. Inaddition, “A part” or “%” indicates a weight basis unless otherwisenoted.

Example 1

Into a dispersion in which commercially available anatase type titaniumoxide particles (“SSP-20 (manufactured by Sakai Chemical Industry Co.,Ltd.)”) are dispersed in methanol, 40 parts by weight of isopropyltriisostearoyl titanate (PLENACT KR-TTS, manufactured by AjinomotoFine-Techno Co., Ltd, volume average particle diameter of 12 nm) withrespect to 100 parts by weight of the untreated anatase type titaniumoxide particles are added dropwise. Then, the mixture is reacted at 60°C. for 1 hour, and the resultant is sprayed and dried at an outer porttemperature of 120° C., thereby obtaining a dry powder. A heatingtreatment is performed on the obtained dry powder in an electric furnaceat 400° C. for one hour, thereby obtaining a titanium oxide particle 1.

Example 2

A titanium oxide particle 2 is prepared in the same manner as in Example1 except that isopropyl triisostearoyl titanate in Example 1 is changedto tetraoctyl bis(ditridecyl phosphite)titanate (PLENACT KR-46B,manufactured by Ajinomoto Fine-Techno Co., Ltd, represented as “Octyl”in the table).

Example 3

A titanium oxide particle 3 is prepared in the same manner as in Example1 except that isopropyl triisostearoyl titanate in Example 1 is changedto bis(dioctyl pyrophosphate)oxyacetate titanate (PLENACT KR-138S,manufactured by Ajinomoto Fine-Techno Co., Ltd, represented as “Methyl”in the table).

Example 4

A titanium oxide particle 4 is prepared in the same manner as in Example1 except that the added amount of isopropyl triisostearoyl titanate inExample 1 is changed from 40 parts to 50 parts.

Example 5

A titanium oxide particle 5 is obtained in a manner similar to that inExample 1 except that the temperature in the electric furnace when driedparticulate powder in Example 1 is heated is changed from 400° C. to250° C.

Example 6

A titanium oxide particle 6 is obtained in a manner similar to that inExample 1 except that the temperature in the electric furnace when driedparticulate powder in Example 1 is heated is changed from 400° C. to500° C.

Example 7

A titanium oxide particle 7 is prepared in the same manner as in Example1 except that the added amount of isopropyl triisostearoyl titanate inExample 1 is changed from 40 parts to 25 parts.

Example 8

A titanium oxide particle 8 is prepared in the same manner as in Example1 except that the added amount of isopropyl triisostearoyl titanate inExample 1 is changed from 40 parts to 75 parts.

Example 9

A titanium oxide particle 9 is obtained in a manner similar to that inExample 1 except that the anatase type titanium oxide particle inExample 1 is changed to a commercial rutile type titanium oxide particle(“STR-100N (manufactured by Sakai Chemical Industry Co., Ltd.)”, volumeaverage particle diameter of 16 nm).

Example 10

A titanium oxide particle 10 is obtained in a manner similar to that inExample 1 except that the anatase type titanium oxide particle inExample 1 is changed to a titanium oxide particle (volume averageparticle diameter of 80 nm) produced by a sol-gel method.

Example 11

A titanium oxide particle 11 is obtained in a manner similar to that inExample 1 except that the anatase type titanium oxide particle inExample 1 is changed to a titanium oxide particle (volume averageparticle diameter of 200 nm) produced by a sol-gel method.

Example 12

A titanium oxide particle 12 is obtained in a manner similar to that inExample 1 except that the anatase type titanium oxide particle inExample 1 is changed to a titanium oxide particle (volume averageparticle diameter of 800 nm) produced by a sol-gel method.

Comparative Example 1

A commercial anatase type titanium oxide particle (“SSP-20 (manufacturedby Sakai Chemical Industry Co., Ltd.”, volume average particle diameterof 12 nm)) is used as it is as a titanium oxide particle C1.

Comparative Example 2

A commercial rutile type titanium oxide particle (“STR-100N(manufactured by Sakai Chemical Industry Co., Ltd.”, volume averageparticle diameter of 16 nm)) is used as it is as a titanium oxideparticle C2.

Comparative Example 3

The commercial anatase type titanium oxide particle (“SSP-20(manufactured by Sakai Chemical Industry Co., Ltd.”, volume averageparticle diameter of 12 nm)) is heated at 400° C. in an electric furnacefor one hour, thereby a titanium oxide particle C3 is prepared.

Comparative Example 4

The commercial rutile type titanium oxide particle (“STR-100N(manufactured by Sakai Chemical Industry Co., Ltd.”, volume averageparticle diameter of 16 nm)) is heated at 400° C. in an electric furnacefor one hour, thereby a titanium oxide particle C4 is prepared.

Comparative Example 5

A titanium oxide particle C5 is prepared in the same manner as inExample 1 except that the added amount of isopropyl triisostearoyltitanate in Example 1 is changed from 40 parts to 5 parts.

Comparative Example 6

A titanium oxide particle C6 is prepared in the same manner as inExample 1 except that the added amount of isopropyl triisostearoyltitanate in Example 1 is changed from 40 parts to 120 parts.

Comparative Example 7

A titanium oxide particle C7 is obtained in a manner similar to that inExample 2 except that the temperature in the electric furnace when driedparticulate powder in Example 2 is heated is changed from 400° C. to600° C.

Comparative Example 8

A titanium oxide particle C8 is obtained in a manner similar to that inExample 3 except that the temperature in the electric furnace when driedparticulate powder in Example 3 is heated is changed from 400° C. to160° C.

Comparative Example 9

A titanium oxide particle C9 is prepared in the same manner as inExample 1 except that the heating treatment of the dried particulatepowder in Example 1 is not performed.

Measurement

Regarding particles prepared in the respective examples, visibleabsorption spectrum characteristics are confirmed. As a result, theparticles in Examples 1 to 12 and Comparative Examples 5 to 7 absorblight in a range of wavelengths of from 400 nm to 800 nm. Table 1 showsabsorbance at a wavelength of 450 nm, absorbance at a wavelength of 600nm, and absorbance at a wavelength of 750 nm when absorbance at awavelength of 350 nm is set to 1 (“UV-Vis characteristics” in thetable).

The element ratio C/Ti and the element ratio O/Ti on the surface of theparticle by XPS, and the volume average particle diameter (“D50v” in thetable) are measured in accordance with the above-described methods.

The surface of the particle prepared in each of the examples isirradiated with an ultraviolet ray having a wavelength of 352 nm and anirradiation intensity of 1.3 mW/cm² at 25° C. (when the irradiationstarts) for 20 hours. Then (“After irradiation with ultraviolet ray” inthe table), the C/Ti element ratio on the surface of the particle by XPSis measured in accordance with the above-described method, and thereduced amount of the element ratio C/Ti by the irradiation with theultraviolet ray is calculated.

Performance Evaluation of Titanium Oxide Particle

Photocatalyst Activity

Degradability (chromaticity variation) of an ink is evaluated asphotocatalyst activity of the titanium oxide particle in the visiblelight region as follows.

Titanium oxide particles obtained in each of the examples are dispersedin water which includes 4% by weight of methanol, so as to provide asolid concentration of 2% by weight. Then, the dispersion is sprayed andapplied onto a tile (5 cm square). Then, the tile is dried, and thus thetitanium oxide particles are allowed to uniformly adhere to the surfaceof the tile. Then, a diluted ink is sprayed and applied onto the surfacethereof. Then, the tile is dried and thus a test piece is prepared. Thediluted ink is obtained in a manner that a fountain pen ink (INK-30-Rmanufactured by manufactured by Pilot Corporation) is diluted 15 timesin a methanol and water liquid mixture (methanol:water=3:5).

A test piece just after the test piece is prepared is continuouslyirradiated with visible light (10,000 LX (LUX)) for 2 hours by using alight emitting diode (LED) which performs irradiation with visible lighthaving wavelengths of from 400 nm to 800 nm (an absorption wavelengthregion (wavelengths of from 450 nm to 550 nm) of the ink is cut by afilter). At this time, a 5-yen coin is disposed at the center portion ofthe irradiated surface of the test piece, and thus a blocked portion ofthe irradiation is formed.

Regarding the test piece just after being prepared and the test pieceafter irradiation with visible light for 2 hours, hue is measured by aspectral color difference meter (RM200QC manufactured by X-Rite Inc.),and ΔE1 and ΔE2 calculated by the following expression are obtained.Chromaticity E is a value calculated by an express ion ofE={(L*)²+(a*)²+(b*)²}^(0.5). L*, a*, and b* indicate coordinate valuesin an L*a*b* color system.ΔE1=(chromaticity of the irradiated surface after continuous irradiationwith visible light for 2 hours)−(chromaticity of the surface of a testpiece just after the test piece is prepared)ΔE2=(chromaticity of the irradiation-blocked surface after continuousirradiation with visible light for 2 hours)−(chromaticity of the surfaceof the test piece just after the test piece is prepared)

The decoloring variation value ΔE=ΔE1−ΔE2 is obtained from ΔE1 and ΔE2,and the degradability is evaluated based on ΔE as follows.

A: favorable degradability

B: slightly favorable degradability

C: poor degradability

Dispersibility

0.05 g of titanium oxide particles obtained in each of the examples isput into a beaker, and 40 g of methyl ethyl ketone is added. Then, afterdispersing is performed for 10 minutes in an ultrasonic dispersionmachine, particle diameter distribution is measured by NANOTRACK UPA-ST(a dynamic light scattering type particle diameter measuring devicemanufactured by Microtrac Bel). Thus, a distribution state of volumeparticle diameter distribution is classified as follows.

A: one peak in the volume particle diameter distribution is provided,and dispersibility is good.

B: two peaks in the volume particle diameter distribution are provided,but the main peak value is equal to or more than 10 times the other peakvalue. Thus, there is no practical problem in dispersibility.

C: three peaks or more in the volume particle diameter distribution areprovided, and dispersibility is poor.

TABLE 1 Before irradiation with ultraviolet ray Metal compound UV-Vischaracteristics Added Absorbance Absorbance Absorbance amount Heating atat at Material of (parts by temperature wavelength wavelength wavelengthparticle Type weight) (° C.) of 450 nm of 600 nm of 750 nm Example 1Anatase type Isopropyl 40 400 0.46 0.35 0.26 titanium oxide Example 2Anatase type Octyl 40 400 0.48 0.36 0.28 titanium oxide Example 3Anatase type Methyl 40 400 0.52 0.40 0.23 titanium oxide Example 4Anatase type Isopropyl 50 400 0.44 0.32 0.19 titanium oxide Example 5Anatase type Isopropyl 40 250 0.28 0.16 0.10 titanium oxide Example 6Anatase type Isopropyl 40 500 0.38 0.24 0.18 titanium oxide Example 7Anatase type Isopropyl 25 400 0.33 0.22 0.12 titanium oxide Example 8Anatase type Isopropyl 75 400 0.28 0.16 0.09 titanium oxide Example 9Rutile type Isopropyl 40 400 0.39 0.28 0.18 titanium oxide Example 10Sol-gel Isopropyl 40 400 0.52 0.43 0.33 titanium oxide Example 11Sol-gel Isopropyl 40 400 0.60 0.45 0.30 titanium oxide Example 12Sol-gel Isopropyl 40 400 0.50 0.38 0.25 titanium oxide ComparativeAnatase type None None None 0.00 0.00 0.00 Example 1 titanium oxideComparative Rutile type None None None 0.00 0.00 0.00 Example 2 titaniumoxide Comparative Anatase type None None 400 0.00 0.00 0.00 Example 3titanium oxide Comparative Rutile type None None 400 0.00 0.00 0.00Example 4 titanium oxide Comparative Anatase type Isopropyl 5 400 0.020.01 0.01 Example 5 titanium oxide Comparative Anatase type Isopropyl120 400 0.66 0.48 0.28 Example 6 titanium oxide Comparative Anatase typeOctyl 40 600 0.08 0.05 0.02 Example 7 titanium oxide Comparative Anatasetype Methyl 40 160 0.01 0.01 0.00 Example 8 titanium oxide ComparativeAnatase type Isopropyl 40 None 0.00 0.00 0.00 Example 9 titanium oxideBefore irradiation with After irradiation ultraviolet ray withultraviolet ray XPS XPS Reduced Element Element Element amount ofEvaluation ratio ratio D50v ratio element Photocatalyst C/Ti O/Ti (μm)C/Ti ratio C/Ti activation Dispersibility Example 1 0.70 2.24 12 0.350.35 A A Example 2 0.77 2.28 12 0.40 0.37 A A Example 3 0.68 2.22 120.25 0.43 A A Example 4 0.90 2.33 12 0.44 0.46 A A Example 5 1.03 2.1012 0.78 0.25 B A Example 6 0.46 2.09 12 0.23 0.23 B A Example 7 0.252.07 12 0.13 0.12 B A Example 8 0.98 2.40 12 0.50 0.48 B A Example 90.65 2.15 16 0.35 0.30 A A Example 10 1.05 2.25 80 0.20 0.85 A A Example11 0.88 2.12 200 0.25 0.63 A A Example 12 0.85 2.45 800 0.73 0.12 B AComparative 0.09 2.00 12 0.06 0.02 C C Example 1 Comparative 0.06 1.9816 0.05 0.01 C C Example 2 Comparative 0.05 2.01 12 0.04 0.01 C CExample 3 Comparative 0.04 2.02 16 0.04 0.00 C C Example 4 Comparative0.16 1.99 12 0.13 0.03 C C Example 5 Comparative 1.31 2.65 12 1.29 0.02C B Example 6 Comparative 0.12 2.01 12 0.10 0.02 C C Example 7Comparative 1.22 2.02 12 1.12 0.10 C B Example 8 Comparative 1.35 2.0112 1.33 0.02 C A Example 9

It is apparent from the above results that photocatalyst activity in theexamples is better than that in the comparative examples. Thus, it isapparent that the examples show a high photocatalyst function even inthe visible light region as compared to the comparative examples. It isapparent that the examples also improve in dispersibility.

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A titanium oxide particle comprising: a metalcompound, which includes a titanium metal atom and a carbon atom bondedto a surface of the titanium oxide particle via an oxygen atom, whereinan element ratio (C/Ti) between carbon and titanium on a surface of theparticle is in a range of 0.2 to 1.1, and wherein the titanium oxideparticle has an absorption at a wavelength of each of 450 nm and 750 nmin a visible absorption spectrum.
 2. The titanium oxide particleaccording to claim 1, wherein the titanium oxide particle has anabsorption in a whole range of wavelengths of from 400 nm to 800 nm inthe visible absorption spectrum.
 3. The titanium oxide particleaccording to claim 1, wherein an element ratio (O/Ti) between oxygen andtitanium on the surface is in a range of 2.05 to 2.50.
 4. The titaniumoxide particle according to claim 1, wherein the carbon atom is includedin a saturated aliphatic hydrocarbon group having 1 to 20 carbon atoms,an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms,or an aromatic hydrocarbon group having 6 to 20 carbon atoms.
 5. Thetitanium oxide particle according to claim 1, wherein the carbon atom isincluded in a saturated aliphatic hydrocarbon group having 1 to 20carbon atoms.
 6. The titanium oxide particle according to claim 1,wherein the carbon atom is included in a saturated aliphatic hydrocarbongroup having 4 to 10 carbon atoms.
 7. The titanium oxide particleaccording to claim 1, wherein a volume average particle diameter of thetitanium oxide particles is in a range of 10 nm to 1 μm.
 8. The titaniumoxide particle according to claim 1, wherein an element ratio (O/Ti)between oxygen and titanium on the surface is in a range of 2.10 to2.40.
 9. The titanium oxide particle according to claim 1, wherein anelement ratio (C/Ti) between carbon and titanium on the surface is in arange of 0.3 to 1.0.
 10. A composition for forming a photocatalyst,comprising: the titanium oxide particle according to claim 1; and atleast one compound selected from the group consisting of a dispersionmedium and a binder.
 11. A photocatalyst comprising: the titanium oxideparticle according to claim 1.